Bulbar
Focus Tube
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Glass-backed Aluminum cathode |
Platinum target |
Aluminium
rod anode |
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Bulbar Focus Tube
dating probably to the early decades 20th Century. 11” (27 cms)
long, 3.5” (8cms) bulb. Unknown make. Aluminium rod anode. Concave
aluminium cathode. Round thin platinum
target, embedded in the anti-cathode and held in place by 4 small metal
claws. No regeneration device. External connection between the
anode and the anti-cathode. Note the glass
backing of the cathode cup, in continuity with the thin glass sleeve around the
stem of the cathode, offering a perfect fit and a stable position of the
cathode structure. Note also the glass sleeving around the anti-cathode stem. Similar tubes were
described “for use with static machines and induction coils producing a
spark discharge 8 to 10 cms long, and are especially suited to the needs of
the average educational laboratory....The penetration of the X-rays produced
is sufficient for viewing the bones of the hand and wrist....” |
In this
tube, and other focus tubes, the anti-cathode lies at a small distance beyond
the focal point of the electron beam. Unlike light rays which diverge after
their focal point, the electron beam emitted by the concave cathode, after
coming to focus, travels for a certain distance in a parallel, pencil-like
beam, making the position of the target uncritical. |
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